Overload switch



s. R. WRIGHT OVERLOAD SWITCH Oct. 9, 1934.

Filed May 11. 1931 7 Sheets-Sheet l Get. 9, 1934. s wRlGHT 1,975,821

OVERLOAD SWITCH Filed May 11. 1931 7 Sheets-Sheet 2 v @MMWCM WM $6M Oct. 9, 1934. s, R. WRIGHT 1,975,821

OVERLOAD SWITCH Filed May 11. 1931 7 Sheets-Sheet 3 35% Mm ym 06L 9, 1934. s R w HT 1,975,821

QVERLOAD SWITCH Filed May 11, 1951 '7 Sheets-Sheet 4 f J0. Wm @(MM 8mm sbxw N W 83% WW S. R. WRIGHT OVERLOAD swncn Oct. 9, 1934.

'7 Sheets-Sheet 5 Filed May 11. 1931 1/ Q a W m HH M a h w o d a u 6mm mg M 5 4m m M mm O 7 X r//nm.... y

s. R. WRIGHT Oct. 9, 1934.

OVERLOAD SWITCH Filed May 11. 1931 a 7 Sheets-Sheet 6 1934- s.' R. WRIGHT 1,975,821

OVERLOAD SWITCH Filed May 11. 1931 '7 Sheets-Sheet 7 4a 45 4? J .5 C

Patented Oct. .9, 1934 UNITED STATES PATENT OFFICE Application May 11, 1931, Serial No. 536,423 In Great Britain May 28, 1930 Claims. (Cl. 200-103) This invention relates to overload switches. The object of the invention is the provision of improvements in such switches and the inven tion consists broadly in the arrangement that upon the occurrence of a relatively low overload the switch is operated after a time\interval in opposition to a retarding device and .upon the occurrence of a relatively hig overload said switch is operated instantly independently of said retarding device.

In order that the invention may be the more clearly understood a number of embodiments thereof will now be described reference being made to the accompanying drawings wherein:-

Fig. 1 is an elevation of an overload switch arrangement in accordance with the invention,

Fig. 2 is a plan of the same,

Fig. 3 is an elevation at a different angle from Fig. 1 of a portion of the same,

Fig. 4 is a sectional elevation of a dash p'ot included in the same.

Fig. 5 is a developed diagrammatic view of a modified arrangement in which protection is also given against voltage failure.

Fig. 6 is a similar view of a still further modified arrangement.

Figs. '7 and 8 illustrate to an enlarged scale in two different positions a lock out element employed in the switches of Fig. 6.

Figs. 9 and 10 illustrate in two positions a modification of the arrangement shown in Figs. 6 to 8.

Fig. 11 is a front elevation of another overload, no volt switch arrangement in accordance with the invention.

Fig. 12 is a plan of the same,

Fig. 13 is an end elevation of the same,

Fig. 14 is a circuit diagram illustrating the way in which the arrangement of Figs. 11-13 is employed when two wire control is required.

Fig. 15 is a similar diagram illustrating the way in which said arrangement is employed when three wire control may be employed.

Fig. 16 is a sectional elevation 01' another overload no v'olt switch arrangement in accordance with the invention.

Fig. 17 is a circuit diagram illustrating the way in which the arrangement of Fig. 16 is employed.

Referring first to Figs. 1 to 4, the arrangement therein illustrated comprises three upright coils 1 for the three phases to be controlled, having magnetic plungers 2 and disposed symmetrically around the iron stem 3 of an upright oil dashpot 4 having a brass plunger. The upper ends of the three plungers 2 have reduced stems 5 55 extending from them and these stems together with the iron dashpot stem 3 are fixed as shewn to a common linking plate 6 so that the three coil plungers and the dashpot plunger are constrained to move as one piece...

On the top of the three coils is located a plate armature 7. This armature 7 has three holes in it through which the coil-plunger stems 5 pass and a. central hole through which the dashpot stem 3 passes. Three short brass sleeves 8 extend downwards from said armature in such a posi tion that their bores form continuations ot the three former holes so that the coil-plunger stems .5 also pass through said brass sleeves. Coil springs 9 surrounding said brass sleeves normally hold the armature 7 a given distance above the top of the coils 1 but if a downward force of con-' siderable magnitude is applied to said armature said springs will be compressed, said brass sleeves passing into the clearance between the coil-plunger stems 5 and the coils.

Three contacts 10 are mounted on the edge of the armature 7 in such a way that their contacting surfaces face outwardly or away from the axis of the dash-pot stem 3. The respective terminals 10a connected to these contacts 10 are mounted on 30 the top of the armature 7 and the contacts, when said armature is in the normal position engage with respective fixed contacts 11. The pairs of contacts 10, 11 are connected in series with one another in the coil circuit of a main contactor or 35 similar isolating switch.

In operation when a current is flowing in the three coils 1 lines of force will pass say up the magnetic plungers 2 and down the magnetic dashpot stem 3 but until the current is large no appreciable number of these lines or force will traverse the armature 7 which is held a considerable distance above the coils.

When this current is normal the upward force on the plungers 2 will be insuflicient to move them and the dash-pot plunger and the contacts 10, 11 will remain in engagement. When, however, this current reaches overload degree the upward force will be suflicient to raise said coil plungers 2 together with the dash-pot plunger and the same will move slowly upward under the restraining influence of the dash-pot. When they have moved a given distance the upper ends of the coil plungers 2 will contact with the lower ends of the brass sleeves 8 and the armature 7 together with the contacts 10 mounted thereon will be raised. These contacts 10 will accordingly break contact with the fixed contacts 11 thereby de-energizing the coil of the main contactor whereupon the cir- Quit of all the phases will be interrupted and all the parts will return to the original position under gravity.

If the current reaches a high degree of overload an appreciable number of the lines of force in the magnetic circuit will traverse the armature 7 with the resultthat the same will be instantly attracted to the coils 1 in opposition to the coil springs 9 before the dash-pot plunger has had time to move, and the movable contacts 10 will break contact with the fixed contacts 11 by moving downwardly instead of upwardly as heretofore. The circuits being thus broken the armature 7 will be released and will move upwards under the influence of the springsi).

If the excessive overload occurs in one coil only, only the portion of the armature '7 above that coil will be attracted, so that the armature will be tilted and one pair of contacts 10, 11 will be opened thereby again breaking the contactor coil circuit.

A suitable mounting for the device may consist of a triangular plate 12 on whose upper face the lower ends of the coils 1 are mounted and on whose lower face the upper end of the dash-pot cylinder 4 is mounted, said plate 12 having holes in it for giving access to the plungers and the dash-pot stem.

The dash-pot has a. variable time lag period after which it's plunger 13 moves freely for permitting the coil plungers 2. to engage with the brass sleeves 8. To this end the bore of the cylinder 4 or dash-pot proper is enlarged toward 1 the upper end as shown so that a clearance is pro- 1 vided outside the circumferential periphery of the piston or plunger when it reaches this enlarged portion of the bore. This piston is formedin the well known way with a downwardly extending skirt and this skirt .has a number of relatively large side holes 14 formedthrough it at a given distance from the top. Top" holes 15 are also formed through the top portion of the piston and a washer 16 is located on this top portion so as to restrict the flow of oil through these top holes when the plunger 13 is being lifted but to permit of 4 free flow when said plunger is sinking. When the plunger is at the bottom of its stroke the side holes 14 will be closed by the wall of the cylinder 4 and the initial upward movement will be slow as governed by the restricted flow of oil through the top holes 15. When however the plunger has been lifted to a given levelthe side holes 14 will register with the enlarged portion of the cylinder bore so that oil with be free to rush through these side holes and the plunger will then rise freely.

' A screwed rod 17 is screwed from the outside 1 through the centre of the bottom of the cylinder ,4. and the upper end of this rod forms a stop limiting the downward movement of the plunger 13 and therefore determining the distance the piston moves at the slow rate or in other words the period of the time lag. By adjusting this screw 1'7, this time lag period may obviously be preselected.

In the arrangement shown in Fig. 5 coils 1 and plungers 2 having reduced stems 5 are provided as before. In this case however the stems 5 pass through a fixed guide plate 18, and a common horizontal wrought iron plate armature 19 is located underneath the three coils. Extending upwardly from this armature is another vertical stem 20 which also passes through a hole in the guide plate 18. The coils and plungers may be arranged symmetrically around the stem 20 as centre.

The upper ends of the three stems 5 of the stem 20 co-act with respective switches 21 and 22 switch 21 is closed and when the common armature 19 is at its lifted position its respective switch 22 is opened.

The common armature 19 is connected, by

means of a divided rod whose two parts 240. and 24b are normally drawn into contact by means of a spring 25 coiled about them, to the plunger of a dash-pot 4a located underneath, which plunger is retarded in respect of its upward movement. This dash-pot 4a may be similar in all respects to the dash-pot 4 described in connection with the preceding arrangement.

.A start push button 26 is provided which short circuits all the four switches 21, 22 so that when this push button is depressed the main contactor winding 23 is energized and the motor is started. The normal current in the three windings will be sufficient to lift the three plungers so that the three plunger switches 21 will close but this normal current will be insufiicient to lift the common armature 19 in opposition to the dash-pot 4a so that the armature switch 22 will remain closed. All four switches 21, 22 being closed therefore the start switch 26 will be short circuited and the contactor winding 23 will remain energized when said short switch is released.

Should the voltage fail in any one of the phases 4a, the lifting force not being great enough to separate the two parts 24a, 24b of the plunger rod by extending said coil spring 25; and when said armature '19 is lifted to its uppermost position the armature switch 22 will be opened and the circuit of the contactor winding 23 again interrupted."

Upon the occurrence of a high degree of overload due say to a short circuit, the lifting force upon said common armature 19 will be sufilcient' to separate the two parts 24a, 24b of the plunger rod by extending said coil spring 25 so that said armature will'be lifted substantially instantaneously to open the armature switch 22.

'The reference 27 designates a stop switch by depression of which the circuit of the winding 23 will be at any time deenergized, thereby oausing the wholearrangement to return to the original position.

Referring now to Fig. 6 this illustrates a somewhat different arrangement in which the separate parallel circuit for the start switch may be dispensed with. In this arrangement there are only the three switches 21, one of these (the centre one according to the drawings) being common as shown to one of the plunger stems 5 and to the armature stem 20. Each of these switches 21 has a lower contact pivoted about point a: and an upper contact pivoted about point y, which upper contact rests upon said lower contact. The three plunger stems 5 act directly to lift the lower contacts and the upper contacts are accordingly lifted by means of said lower contacts. The armature stem acts directly to lift the upper contact of the switch to which it appertains.

The lower contact of each switch 21 has a tall piece as shown which interlocks with a tail piece on the upper contact of the switch 21 immediately to the left in such a way that said upper contact cannot fall so long as said lower contact of the former switch is held up. (As the drawing is a developed diagrammatic drawing it has not been possible to illustrate thisinterlock in the case of the two switches which appear as being outside in said drawing.)

Each of the three switches 21 is provided with a weight biased lock-out element 28 (Figs. '7 and 8) pivoted, about an axis 2, on the upper contact, which, immediately the two contacts are sufiiciently separated to break circuit, is free to rotate under the influence of its biasing weight from the position of Fig. '7 to insert an insulating piece 29 between them as in Fig. 8. A common resetting arm 30 is provided upon operation of which any of these lock-out elements are reset.

In this case the start switch 26a is an ordinary switch and is connected in series with the three switches.

This start switch 26a being open, the contactor .winding 23 and the motor power circuit will be de-energized, the three plungers 2 and the armature 19 will be at the down position and both contacts of each switch 21 will be at the down position and therefore in contact with one another.

Therefore when the start switch 26 is closed the circuit for the contactor winding 23 will be energized and the motor started, and when the consequent energization of the three windings 1 causes the plungers 2 to rise, the lower contacts of the switches 21 will be lifted and will lift the upper contacts and remain in contact therewith.

Should voltage failure occur in any phase the corresponding plunger 2 will drop and the lower contact of the corresponding switch 21 will also drop. So long as this contact is actually making contact with the upper contact however, the upper contact will not drop with it owing to the interlock with one of the other switches 21, and immediately the two contacts are sufficiently separated to break contact the insulating piece 29 will be inserted as above described so that the circuit will be permanently broken until the resetting bar 30 is actuated.

When overload occurs it is clear that upon the upper contact of the centre switch 21 being.

lifted by the stem 20 the insulating piece 29 will in like manner be interposed between the two contacts.

When however the start switch 26a is opened so that all the contacts drop together. they will remain in contact with one another so that the circuit is ready to be re-establlshed immediately by reclosure of said start switch.

The arrangement of Figs. 6-8 may be modified as in Figs. 9 and 10. In this latter arrangement as before the two elements of each of the switches 21 are pivoted about axes r and ya through which axes the series connection of the switches is established and each right hand switch element has a tail piece which engages under a tail piece on the left hand switch element of the switch immediately to its right. Each of these right hand tail pieces is upwardly biased by means of a spring 31 and since the left hand tailpieees rest on the right hand tail pieces it will be seen that all the tail pieces are upwardly biased with one equal force. Normally these upwards biases bal ance each other by the engagement of the opposite contacting surfaces of the switch elements as shown in Fig. 9 and the whole arrangement is in equilibrium andin readiness for the establishment of circuit for the contactor winding when the start switch is closed. When said start switch is closed the three plunger windings will be energized and the stems 5 will rise simultaneously These stems carry bridging contacts 32 at their upper ends and when said stems rise said bridging contacts simultaneously enter between the contacting surfaces of the switch elements forcing the latter apart and thereby forcing the tail pieces downwardly in opposition to the springs 31. The current thus remains unbroken and if the start switch is switched on so that the plungers all fall at once the tail pieces are all free to rise together and the contacting surfaces will come together simultaneously once more at the position of Fig. 9. If, however, owing to the voltage failure only one plunger commences to fall, only the tail pieces of the left hand element appertaining to that particular switch 21 will be free at the moment to rise (under gravity) and therefore only the left hand contact will begin to fall inwardly without the right. This causes an insulating tip 33 on said left hand contact to engage with the right hand contact (as shown in Fig. 10) the instant the contacts disengage so that as in the preceding arrangement the circuit is permanently'broken until reset.

In this arrangement an overload arrangement similar to that of Figs. 5 and 6 is employed but the stem 20 actuates a separate overload switch not shown.

In the arrangement illustrated in Figs. 11 to 14 a single switch is provided in place of the three plunger switches. The movable contact of thisswitch takes the form of a V shape plate 34 pivoted about a horizontal axis X-X in its plane and passing say through'the apex of the V parallel to an imaginary line joining the extremities of the two arms. The stems 5 of the three plungers 2 are formed with collars 35 which engage each with an insulating end of a respective rocking element 36 pivoted between its ends about a horizontal axis in such a way that when said plungers 2 are pulled down the said insulating ends of said pivoted elements 36 are pulled down and the remote ends ofsaid pivoted elements are accordingly pushed up.

This arrangement is provided with an armature 19, armature stem 20, divided rod 24a, 241) spring 25 and dashpot 4a all functioning precisely as in Figs. 5 and 6, the arrangement being such that when the armature 19 is lifted the stem 20 135 lifts the V shaped bridging contact 34.

The V shape bridging contact 34 is biased by means of a spring 3'7 about its axis in such a way that the extremities of its two arms bear down upon the remote ends of the two outer rocking 140 elements 36 and the crutch portion of said bridging contact 34 bears down on the remote end of the third rocking element 36. The remote ends of said two outer rocking elements 36 carry contact pieces 360. which are engaged by similar 14,5 contact pieces 34a on the extremities of the bridging contact 34 and the contact pieces 36a. are connected through the pivotal bearings of the respective elements 36 with fixed terminals 38. These terminals 38 are connected in series with 150 switch 26a across lines L3, L1.

1o gized and its contacts 39 accordingly closed. Closure of said relay contacts 39 establishes circuit for the main contactor winding 23 through the two terminals 38, the conducting portions of the two outside rocking elements 36 and the V shaped l5 bridging contact 34 whose extremities are pressed down on to the raised remote contact bearing ends of said rocking elements 36.

The contactor accordingly closes its contacts 23a; the motor is started, the three coils 1 energized and the three plungers 2 and their stems 5 accordingly raised to their up'position. This will permit the remote ends of the rocking elements 36 to be pressed down by means of the V shaped bridging contact 34, contact being main- 25 tained throughout between the contact pieces 34a and the contact pieces 36a so that the circuit of the main contactor winding 23 will remain 'unbroken.

If nonvoltage failure occurs in any one phase the plunger 2 appertaining to that phase will" fall and the remote end of the respective rocking element 36 will accordingly be raised thereby raising the V shaped bridging contact 34 out of contact with the other rocking elements 36 and accordingly breaking the circuit of the main con- 1 tactor winding 23. It will be observed that owing to the circuit connections, said main contactor ,winding cannot be re-energized until the failure has been remedied. Thus so long as there is 6.9 voltage failure in the phase L1, neither the relay winding 40 or the main contactor winding 23 can be energized; voltage failure in phase L2 prevents the main contactor winding 23 from being energized, and voltage failure in L3 prevents the relay winding from being energized. Thus until voltage is re-establishd in all three phases the main contactor cannot be reclosed.

Fig. 15 illustrates a slightly modified arrangement in which three wire control may be em- 56 ployed. In thislarmngement the relays 39, 40

are dispensed with aiidanadditional contact 235 is provided on the main contactor which opens and closes according as the main contacts 23a of said main contactor open and close. This additional contact 231) short circuits a start push button 26a connected in series with the V shape bridging contact 34 and the main contactor winding 23 across lines L3, L2. Thus upon pressing said start push button 26a said main contactor 60 winding 23 is energized by a circuit which is maintained upon closure of the contactor 23b independently of said start push button. As before the bridging contact 34 moves down in engagement with the remote contact bearing ends of the rocking element 36 thereby maintaining the contactor winding circuit and said bridging contact is opened upon failure of any one phase. In this case, it is clear that once the contactor is opened its winding 23 cannot be again energized until the start push button 26a is depressed. The

reference 27a designates a stop push button.

In either of these latter cases the raising of the armature stem 20 upon overload lifts the V shape bridging contact 34 and breaks the cir- Cult. In the case of the three wire control in Fig. 15 the circuit cannot be again established until the start push button 26a is depressed. In the case of the two wire control, the bridging contact 34' after being lifted by the armature stem 20 is held up by means of a hand releasable latch Z shown in Fig. 13.

Referring now to Figs. 16 and 17 these illustrate a somewhat simplified arrangement for two wire control. In these figures like references to those employed in Figs. 11 to 13 designate corresponding parts. The device comprises a plate 34a. pivoted about an axis XX and biased downwards by means of a spring 41 toward bridging engagement with a pair of fixed contacts respectively connected to the terminals 38 (Figs. 17). When the plungers 2 are down the collars 35 on the plunger stems 5 bear down each upon one end of a pivoted trip arm 42 thereby causing the remote end of said arm to rise to the up position. The remote end of any of these three trip arms 42 being at the up position the plate 34a is lifted and held at the circuit breaking position.

A second bridging contact 345 is also provided which is biased downwardly to a position at which it bridges two other contacts respectively connected to the terminals 38. This contact 34?) is carried by an arm 43 to which is attached a plate 44 which the collars 35 engage and lift, thereby lifting said contact 34b to the contact breaking position, when the plungers 2 are at the up position. A catch 45 is pivotally mounted on a fixed part and biased about its axis 46 by a spring 47 so that it presses against the edge of said plate 44, and also against the collar 35 of one of the plungers 2 so that only when the said collar 35 is down and said plate 44 is up can said clutch 45 click inwards thereby preventing said plate 44 and therefore said contact 341) from releasing to the closed or down position. The external connections are made as in Fig. 17 the collar 35 which engages with the catch 45 being the one associated with the line L1. Normally, when the switch 260. is open, the plunger 2 being down the plate 34a will be held at the up or open position. The contact 34b will however be at the down or closed position, the whole arrangement being as in Figs. 16 and 17. Where switch 26a is closed circuit will be established from line L2 through winding 23, said switch 26a, the contact 34b, to line L3. The main contacts accordingly close the contacts 23a and the three windings l are energized. The plungers 2 accordingly rise and the timing in is such that first the plate 34a is permitted to close after which the contact 34b is opened. If now circuit fails in either L3 or L2 the plate 34a will move to open position thereby interrupting circuit of coil 23 and open ing the contactor. The other two plungers will now fall and the contact 342) will accordingly reclose, the plate 44 engaging the catch 45 before the collar 35 releases it. Obviously the coil 23 cannot be reenergized until the failure has been rectified. 1

Upon current failure in L1 the collar 35 supporting the catch 45 will fall thereby opening the plate 340. and de-energizing coil 23 as before so that the other two plungers will also fall. In this case, however, since the aforesaid collar 35 falls before the other two it is momentarily down while the plate 44 is still up so that the catch 45 now operates to maintain contact 345 against closing. It is now evident that the coil 23 cannot be again energized until this catch is released and the contact 45 reset.

Upon the occurrence of overload the rod lifts the plate 34 as before the armature 19 being latched up by means of latch Z releasable by member associated with each of said windings,

each of said armature members being responsive to operate said circuit interrupting mechanism upon failure of voltage in its associated winding,

and an armature member common to said windings, said latter armature being responsive to a circuit interrupting mechanism, an armature member associated with each of said windings, each of said armature members being responsive upon failure of voltage in its associated winding to effect operation of said circuit interrupting mechanism, an armature member common to said windings and responsive to eflect operation of said circuit interrupting mechanism, said latter armature being responsive after a given period of delay upon given current conditions in any one orall of said windings and being also responsive substantially instantaneously upon given increased current conditions in any or all of said windings.

3. The combination with a polyphase alternating current circuit, of a protective device therefor including a switch mechanism operable to effect interruption of said circuit, a plurality of electromagnetic windings connected in difierent phases of said circuit, an armature member common to said windings and responsive under the action thereof to operate said switch mechanism for interruption of said circuit upon overload conditions in any or all of the phases thereof, and means for delaaiing response of said armature member under low overload conditions in said circuit and for permitting immediate .response thereof under heavy overload conditions in said circuit.

4. In a protective device for polyphase'alter nating current circuits, in combination, a switch including a plurality of terminal contacts and a cooperating bridging contact, a plurality of windings to be supplied with currents of unlike phase, means under the control oi said windings for efectirig bridging of said terminal contacts by said bridging contact upon energization or deenergization 01 said windings simultaneously and for also efiecting unbridging of said terminal contacts by said bridging contact upon deenergization 01' any one of said windings with the other of said windings energized, and an armature member common to said windings and responsive to eflfect unbridging of said terminal contacts by said bridging contact upon given overload current values in any or all of said windings.

5. In a protective device for polyphase alternating current circuits, in-combination a plurality of electromagnetic windings to be supplied with currents of unlikephase, a normally clgsed circuit interrupting mechanism, means under the control of said windings for maintaining said circuit interrupting mechanism in closed position upon simultaneous energization of all of said windings, and for effecting opening of said circuit interrupting mechanism upon failure of no voltage in any one of said windings with the other of said windings energized, and an armature member common to said windings and responsive under the action thereof to efiect opening of said circuit interrupting mechanism, said armature member being responsive after. a given period of delay upon given overload conditions in any or all of said windings, and being also responsive substantially instantaneously upon given increased overload conditions in any or all of said windings.

' STANLEY ROBERT WRIGHT. 

